Metalworking fluids, such as lubricants and coolants, are widely used to provide more efficient metal process operations such as cutting, turning, drilling, grinding, milling, rolling and the like. Such fluids function to lubricate and cool the metal and tools used in the metalworking operations, and to facilitate removal of chips during turning, grinding, and similar operations. They can also be used to protect metals and tools against corrosion and rust formation. Metalworking fluids are important to many machine operations, because they increase production outputs, increase tool life, and enhance surface finish of the metal pieces being processed.
Metalworking fluids used to date generally fall into four categories: (1) straight oils, usually light mineral oils or kerosene; (2) soluble oils, also referred to as water-soluble emulsions, which contain oil and surfactants for emulsifying the oil; (3) semi-synthetic types, which contain relatively small amounts of oil and large percentages of surfactants or detergents and are typically provided as an oil-in-water emulsion; and (4) synthetic or chemical types, which contain no oil, but rely on various chemical compounds to achieve desired properties. The metalworking fluid formulations in the first three categories usually require surfactants for reducing surface tension.
Metalworking fluids are susceptible to the infestation and growth of microorganisms such as bacteria, fungi and yeast. Frequently, these microorganisms can cause the buildup of slime and sludge, the clogging of lines and filters, the deterioration of the properties of the metalworking fluid itself, facilitated corrosion, and health and odor problems. When affected or deteriorated by the growth of microorganisms, the metalworking fluid loses many of its essential properties. The pH of the fluid may drop and other chemical changes may occur until the fluid can no longer impart adequate lubricating, cooling or anti-corrosive properties. At this point, the fluid must be replaced with fresh metalworking fluid, which is costly.
It has been a conventional practice to add bactericides to metalworking fluids to minimize the microbial degradation of such fluids. For example, formalin or compounds giving off formalin are well-known antimicrobial agents used in metalworking fluids. However, since formalin is questionable from health and environmental aspects, there is every reason to avoid the use of formalin or compounds giving off formalin. Quaternary ammonium compounds, alkanolamine compounds and secondary amine compounds are also known antimicrobial agents. See for example U.S. Pat. Nos. 4,925,582, 5,132,046, 5,512,191 and 5,633,222.
Iodopropargyl compounds, which contain a propargyl group and iodine, are known to be useful in controlling bacteria and fungi in metalworking fluids. U.S. Pat. Nos. 4,719,227, 4,945,109 and 5,179,127 disclose various iodopropargyl compounds useful as microbicidal agents for the preservation of metalworking fluids. U.S. Pat. Nos. 5,156,665, 5,328,926 and 5,374,631 disclose synergistic combinations of iodopropargyl compounds and other compounds for the control of fungal or bacterial growth in metalworking fluids.
However, such bactericides as described above may exhibit good biocidal activities against certain microorganisms but may not be effective against other types of microorganisms, resulting in restricted applicability of the bactericides. Moreover, physical conditions, such as high temperatures, and chemical reactivity with ingredients present in the metalworking fluids often diminish or eliminate the effectiveness of the bactericides. For example, many metalworking fluids contain organic materials which may react with a specific bactericide and render the bactericide ineffective. Therefore, the bactericides may decompose or become inactive over time, so that they usually posses a fairly short useful life and need to be replenished often or even completely replaced. In addition, the use of bactericides at high concentrations imposes adverse effects on the human body, for example, it may cause skin irritation, dermatitis or other health problems. There may also be considerable environmental problems associated with disposal of used metalworking fluids, due in large part to the presence of these additives and other contaminants. Another disadvantage of adding bactericides is that additional manpower or devices are required to maintain a relatively constant concentration of the bactericide in the metalworking fluid.
Apparatuses have been developed in the art for the disinfection of metalworking fluids. U.S. Pat. No. 5,589,138 discloses an apparatus for regenerating metalworking fluids by controlled addition of a chelating agent to sequester metals dissolved in the fluids. The apparatus includes monitoring means for determining the presence of free metal ions in the fluid, testing means for determining the concentration of free metal ions if present, and addition means for adding, in a controlled manner, a chelating agent for sequestering the free metal ions.
U.S. Pat. No. 4,482,462 discloses a device for treating process fluids such as metalworking fluids within a closed chamber with a chemical reactant, preferably a triiodated quaternary amine anion exchange resin. The device includes a compartment for containing the chemical reactant and a port for allowing flow of the process fluid therethrough. The device is characterized by including recirculation means for alternately drawing at least a portion of the process fluid into the compartment through the port to bring the portion of the process fluid into direct contact with the chemical reactant to treat the fluid, e.g., dissolving and/or reacting with a portion of the chemical reactant with the portion of the process fluid. The recirculation means then forces the portion of the process fluid out of the compartment through the same port to circulate the dissolved chemical reactant, such as iodine, through the remaining process fluid within the closed chamber.
U.S. Pat. No. 6,616,835 describes a coolant recycling system comprising a support frame, a first tank for receiving contaminated coolant, a second tank for receiving a volume of water and coolant concentrate, and a third tank for treating and cleaning the contaminated coolant. The third tank is provided with an ozone applicator which applies a specific volume of ozone to the coolant during the mixing of the coolant within the third tank which kills microorganisms.
U.S. Patent Application Publication No. 20030098276 describes a filter and method for removing undesirable particulates and bacteria from metalworking fluids. The method comprises providing an enclosed channel for fluid flow and passing the fluid flow through a filter material comprising a metal alloy consisting primarily of copper and zinc and further comprising metal fiber wools.
However, the prior art apparatuses are complex in construction and operation. Moreover, these apparatuses either involve addition of chemicals into the metalworking fluids or inevitably leave behind chemicals in the treated fluids, which may impose health and environmental problems.
There remains a need for a system that is easy to operate and exhibits prolonged biocidal effects in metalworking fluids without leaving behind unacceptable amount of chemicals in the treated fluids.